A protective hood of the kind described above is disclosed in U.S. Pat. No. 2,435,167. Protective hoods for emergencies are preferably utilized for rescuing persons from rooms which are in danger of burning and in which smoke and dust occur because of the fire. However, these protective hoods also serve to protect the breathing of aircraft passengers who require additional breathing support in the event of decompression in the passenger cabin or in the event that a fire breaks out. The breathing support can be in the form of protection from breathable harmful substances and/or in the enrichment of the breathing air with oxygen.
The known protective hood comprises a material which is permeable to air and water and yet keeps back dust. This known protective hood has an inner half-mask with an inlet opening which opens into the inner space of the hood and through which the person wearing the hood can inhale the air. Exhalation occurs via an exhalation valve which starts at the inner half-mask and opens to the ambient. The finest dust can possibly penetrate through the intermediate spaces of the hood. In order to also keep this fine dust from the respiratory system of the person wearing the hood, the inlet opening is provided with a further dust filter. The flow resistance of this inlet opening must be significantly greater than that of the exhalation valve in order to suppress an inhalation of the exhaled air by the wearer. This makes breathing more difficult.
With known protective hoods, it is a disadvantage that they can only protect the person wearing the hood against dust with an inlet opening having a considerable inhalation resistance being necessary to keep back the finest dust. Also, there is no protection against gaseous harmful substances which penetrate the fabric of the hood and can irritate the eyes and skin as well as impair breathing. The protruding configuration of the inhalation opening and outlet valve prevent the entire hood from being packed in a space-saving manner and is therefore restrictive in the tight space relationships present in an aircraft or restrictive when carried by the user.
A further protective hood is disclosed in published German Patent Application DE-OS No. 31 38 697.
This protective hood serves to completely cover the head and is in the form of a hood made of a fabric which is configured as a filter by means of interlayered active charcoal. A tunnel-like spacer is attachable over the mouth-nose region to prevent the body of the hood from lying tightly against the nose and mouth of the person wearing the hood. If the body of the hood were permitted to lie against the nose and mouth, free breathing would be prevented and a premature exhaustion of the protective effect through excessive respiration would occur.
Breathing occurs over the entire surface of the hood with the inhalation as well as the exhalation taking place undirected across the intermediate space between the head of the wearer and the hood itself. This causes an undesired high respirated dead space to occur which can lead to excessive enrichment with carbon dioxide and water vapor with long continuous breathing activity.